Structural formwork member

ABSTRACT

A structural formwork member is disclosed. The structural formwork member includes a base member in the form of a profiled metal sheet that has parallel ribs ( 5 ) and plurality of pans ( 6 ) between the ribs. The structural member also includes a strengthening member ( 71 ) that is structurally connected to the base member.

[0001] The present invention relates to structural formwork members andto composite slabs that include the structural formwork members.

[0002] The present invention relates particularly to structural formworkmembers for constructing composite slabs.

[0003] A major, although not the only, end use application of suchstructural formwork members is in the construction of composite slabsthat form floors in buildings (which term includes car parks).

[0004] Another, although not the only other, end use application of suchformwork members is in the construction of composite slabs that formvertical wall panels.

[0005] One type of structural formwork member for constructing compositeslabs that form floors of buildings includes:

[0006] (a) a base member in the form of a profiled steel sheet that hasparallel ribs separated by pans; and

[0007] (b) strengthening members in the form of lattice girders formedfrom top chord elements that are spaced above the sheet and web chordelements that are welded to the top chord elements and to the ribsand/or pans of the sheet.

[0008] The lattice girders may also include bottom chord elements thatare parallel to the top chord elements.

[0009] Examples of the above-described type of structural formworkmember and composite slab formed from the member are disclosed inJapanese patent application JP,A,4-222739 (Hory corporation) andAustralian patent 707101 (The Broken Hill Proprietary Company Limited).

[0010] The structural formwork members and the composite slabs formedfrom the members that are described and claimed in Australian patent707101 are marketed by the applicant under the trade mark TRUSSDEK.

[0011] In the arrangements disclosed in the Japanese patent applicationand the Australian patent the steel sheet, the top chord elements, andthe web chord elements (and the bottom chord elements, when present)define a series of spaced apart trusses that extend along the length ofthe sheet.

[0012] In use, the structural formwork members are laid on and sometimesare secured to floor supports and concrete is poured in situ to completeconstruction of composite floor slabs.

[0013] Accordingly, each composite floor slab includes a structuralformwork member and a layer of concrete on the base member of thestructural formwork member.

[0014] The structural formwork members may be constructed to extendacross a span between adjacent temporary or permanent floor supportswith the ends of the formwork members resting on the floor supports.

[0015] The structural formwork members may also be constructed to extendacross multiple spans between temporary or permanent floor supports withthe ends of the formwork members resting on the outermost floor supportsand intermediate sections of the formwork members resting on one or morefloor supports that are between the outermost floor supports.

[0016] The inventors have carried out extensive research and developmentwork on TRUSSDEK structural formwork members and TRUSSDEK compositefloor slabs formed from the members.

[0017] One outcome of the research and development work is that theinventors have made a number of improvements to the TRUSSDEK structuralformwork member and have invented an improved structural formworkmember.

[0018] In general terms, the improved structural formwork member of thepresent invention includes:

[0019] (a) a base member in the form of a metal sheet; and

[0020] (b) at least one strengthening member that is structurallyconnected to the base member.

[0021] Preferably the metal sheet is a steel sheet.

[0022] The base member may be in the form of a flat sheet.

[0023] The base member may be in the form of a profiled sheet that hasparallel ribs that extend along the length of the base member and aplurality of pans between the ribs.

[0024] Preferably the pans are flat.

[0025] The strengthening member may be located in one of the pans.

[0026] Alternatively, the strengthening member may be located in twoadjacent pans and straddle the rib between the pans.

[0027] Preferably the ribs of the base member are small ribs.

[0028] The applicant has found that small ribs make a significantcontribution to the compressive capacity of the profiled sheet inregions where there is global negative bending along the length of thesheet.

[0029] Typically, there is negative bending in sections of the profiledsheet that are directly over or are proximate to temporary or permanentsupports for the structural formwork member.

[0030] This is an important issue with increasing unsupported spanlengths of a structural formwork member of a given sheet thickness.

[0031] This is also an important issue with decreasing sheet thicknessof a structural support member spanning a given span length.

[0032] The applicant has also found that small ribs make it possible touse the structural formwork member in the construction of compositeslabs that will be subject to significant 2-way bending action andtherefore require a significant amount of reinforcement or pre-stressingin a direction transverse to the strengthening member to strengthen thecomposite slabs.

[0033] The applicant has also found that small ribs do not affectadversely the shear performance of shear connectors that are used toconnect composite slabs to supports.

[0034] It is preferred that the height of the ribs above the pans be nomore than 20 mm.

[0035] It is preferred particularly that the height of the ribs abovethe pans be no more than 15 mm.

[0036] It is preferred more particularly that the height of the ribsabove the pans be no more than 10 mm.

[0037] It is preferred that the height of the ribs above the pans be nomore than 20% of the height of the strengthening member above the pans.

[0038] It is preferred particularly that the height of the ribs abovethe pans be no more than 15% of the height of the strengthening memberabove the pans.

[0039] It is preferred that the height and the number of the ribs beselected so that the width of the profiled sheet is at least 80% of thewidth of a flat sheet prior to forming the ribs in the flat sheet andproducing the profiled sheet.

[0040] It is preferred that the shape of the ribs facilitateinterlocking of the base member and concrete that in use is poured ontoand sets on the base member to form a composite slab.

[0041] Preferably the lengthwise extending sides of the base memberinclude male and female formations that enable a plurality of thestructural formwork members to be positioned in side by side overlappingrelationship with the male member of one member and the female member ofan adjacent member forming a lap joint.

[0042] The base member and the strengthening member may form a trussthat extends along the length of the base member.

[0043] The strengthening member may include a lattice girder formed froma top chord element that is spaced above the base member and web chordelements that are connected to the top chord element and to the ribsand/or pans of the base member.

[0044] The lattice girder may also include bottom chord elements thatare parallel to the top chord element and are connected to the web chordelements.

[0045] The strengthening member may also be in the form of an invertedchannel member.

[0046] Preferably the inverted channel member has a top wall and twosides, with the sides being connected to the base member and the topwall being spaced above the base member.

[0047] Preferably the channel member is formed from a roll-formed metalsheet.

[0048] Preferably the channel member is formed from a roll-formed steelsheet.

[0049] Preferably the roll-formed steel sheet is 0.6-1.2 mm thick.

[0050] More preferably the thickness of the roll-formed steel sheet is0.6-0.8 mm.

[0051] Preferably the height of the channel member is 80-240 mm.

[0052] More preferably the height of the channel member is 130-240 mm.

[0053] Preferably the width of the channel member, measured between theconnections of the sides of the channel member to the base member, is90-190 mm.

[0054] Preferably the sides of the channel member converge upwardlytowards the top of channel member.

[0055] Preferably the sides of the channel member have outwardly turnedflanges to improve the connections between the sides of the channelmember and the base member.

[0056] Preferably one or both sides of the channel member includesections that are pressed or otherwise formed out of the plane of theside or sides to provide resistance to local buckling of the structuralformwork member and to increase the shear capacity of the structuralformwork member.

[0057] Preferably the pressed sections are ribs or corrugations in theside or sides.

[0058] Preferably the axes of the ribs extend transversely to thelengthwise direction of the base member.

[0059] Preferably the crests and the troughs of the corrugations extendtransversely to the lengthwise direction of the base member.

[0060] Preferably the depth of the corrugations, measured between theapices of the crests and the bases of the troughs, is at least 3 mm.

[0061] Preferably the wavelength of the corrugations, measured betweenapices of adjacent crests or between bases of adjacent troughs, is 30-60mm.

[0062] The channel member and the base member may define a waterimpermeable void to minimise transverse deflection of the structuralformwork member when wet concrete is poured onto the member in theconstruction of a composite slab and/or to provide an access pathway forbuilding services, such as telecommunications cables, in a compositeslab.

[0063] The term “water impermeable void” is understood herein to mean avolume that cannot be penetrated by wet concrete poured onto astructural formwork member.

[0064] Preferably the void is filled with fire resisting or retardingmaterial.

[0065] Preferably the inner surfaces of the channel member and thesurface of the base member that form the void are coated with a fireresisting or retarding material.

[0066] Preferably the void includes a sound absorbing material.

[0067] Alternatively, one or both sides of the channel member mayinclude openings to allow access to the interior of the channel member,whereby wet concrete can flow into the volume defined by the channelmember and the base member during construction of a composite slab.

[0068] Preferably the sides of the channel member include alignedopenings to allow reinforcing bars/wires/cables to be positioned toextend transversely through the channel member during construction of acomposite slab.

[0069] Preferably the openings are formed to minimise the possibilitythat the openings will weaken the channel member. The openings mayinclude suitable reinforcement.

[0070] Alternatively, the channel member may be formed so that one ormore sections can be filled with concrete and one or more sections canbe voids. For example, the channel member may include openings near theends of the channel member and an internal diaphragm positioned so thatconcrete can only flow into the end sections of the channel member. Thisarrangement prevents the voids from interfering with the integrity ofthe shear connection made between a composite slab and permanent supportbeams.

[0071] Preferably the channel member includes internal or externalbracing members at the ends and/or along the length the channel memberto resist collapse of the channel member by transferring reaction forcesacting on the channel member.

[0072] Preferably the channel member further includes a top chordelement mounted to or retained by the channel member.

[0073] The top chord element may be any suitable member.

[0074] Preferably the top chord element is a bar or a rod or a plate.

[0075] Preferably the top chord element is a steel bar or a steel rod ora steel plate.

[0076] Preferably the plate is deformed, rippled or holed to improvemechanical interlock of the structural formwork member with concrete ina composite slab.

[0077] By way of example, the plate may be deformed by shaping the plateto include up-turned and/or downturned sections.

[0078] The top chord element may be mounted to the channel member by anysuitable means.

[0079] One option is to weld the top chord element to the base of thechannel member.

[0080] Another option is to glue the top chord element to the base ofthe channel member.

[0081] Another option is to mount the top chord element to the channelmember using web chord elements connected to the top chord element andto the channel member.

[0082] Another, although not the only other, option is to mount the topchord element to the base of the channel member using one or morebrackets that are mounted to the channel member and are formed to retainthe top chord element by snap-fit or other suitable engagement.

[0083] Preferably the bracket is in the form of a saddle that has legsthat straddle the channel member and the legs have inwardly directedtabs, and the sides of the channel member have openings that receive thetabs and thereby retain the saddle on the channel member.

[0084] Alternatively, the base of the channel member may be formed to atleast partially enclose and thereby retain the top chord element.

[0085] Preferably the base includes a transverse section that iscomplimentary to that of the top chord element so that the top chordelement can be snap-fitted into engagement with the base.

[0086] The strength of the connection of the top chord element to thechannel member is preferably selected so that the failure made is byyielding the top chord element in tension or compression.

[0087] The structural formwork member may include a bridging member thatis connected to one or both ends of the structural formwork memberand/or at one or more locations along the length of the structuralformwork member to enable direct load transfer from the strengtheningmember to temporary or permanent supports for the structural formworkmember.

[0088] The bridging member is an important feature particularly,although by no means exclusively, in situations in which thestrengthening member includes a top chord element and web chord elementsthat form a truss with the base member. Specifically, the feature takesinto account that the assembly of the top chord element and the webchord elements that form the strengthening member is usually a basicunit of length that is repeated along the length of a structuralformwork member.

[0089] Accordingly, depending on the length of a structural formworkmember, the strengthening member at one or both end sections of theformwork member that rest on temporary or permanent supports may be anend of a unit or partway along the length of a unit. Similarly, if astructural formwork member continues over multiple spans, the samesituation may occur at intermediate temporary or permanent supports.

[0090] The above situation is significant because the structure of thestrengthening member at the end or intermediate sections of a structuralformwork member that rests directly on temporary or permanent supportscan affect load transfer between the member and the temporary orpermanent supports. Less than optimum load transfer may lead to reducedstrength and excessive deflection or local deformation of the structuralformwork member, particularly when concrete is poured onto the member toform a composite slab.

[0091] The use of the bridging member makes it possible to use standardconstruction lengths of structural formwork members in a range ofnon-standard span length situations without compromising load transferbetween the structural formwork member and temporary or permanentsupports.

[0092] The bridging member may be in the form of a chord elementconnected to a strengthening member.

[0093] The chord element may be in the form of a frame.

[0094] The chord element may include a means that permits adjustableconnection of the chord element to the strengthening member.

[0095] The bridging member may also be in the form of a panel, forexample formed from steel sheet or plate.

[0096] The bridging member may also be in the form of an elongatemember, such as a beam and a plate, connected to the base member of thestructural formwork member.

[0097] The structural formwork member may include one or more waterimpermeable voids that contacts a section or sections of the base memberbetween adjacent strengthening members to minimise transverse deflectionof the section when wet concrete is poured onto the structural formworkmember.

[0098] The above-described void feature is based on the applicantrecognising two particular factors that contribute to transversedeflection, i.e. downward bulging, of sections of a base member that arebetween adjacent strengthening members in response to wet concreteloading. The factors are hydrostatic pressure of water in wet concreteacting against the base member and the weight of the wet concrete.

[0099] Downward bulging can be excessive and quite noticeable on theunderside of a structural formwork member and, in addition to detractingfrom the visual appearance, may impinge on the installation of finishesand/or building services. In addition, downward bulging can add to theamount of concrete that is required to form a flat slab surface.

[0100] The applicant has found that the use of a void as described aboveminimises the adverse effect of hydrostatic pressure and concrete weightby making it possible to transfer the load resulting from wet concreteabove a void to or to the region of the strengthening members located atthe sides of the void.

[0101] The void need not function as a structural member.

[0102] However, the structure that defines the void needs to havesufficient stiffness and strength to transfer the load resulting fromwet concrete above the void to or to the region of the adjacentstrengthening members.

[0103] Preferably the void extends across a substantial part of thewidth of a section of a base member that is between adjacentstrengthening members.

[0104] Preferably the void extends across at least 70%, more preferablyat least 80%, of the section of the base member that is between adjacentstrengthening members.

[0105] The structural formwork member may include a plurality of voidsspaced along the length of a section of a base member that is betweenadjacent strengthening members.

[0106] The structural formwork member may also include a single voidextending along the length of a section of a base member that is betweenadjacent strengthening members.

[0107] The void may be small in terms of height so as to make itpossible to use the structural formwork member in the construction ofcomposite slabs that will be subject to significant 2-way bending actionand therefore require a significant amount of reinforcement orpre-stressing in a direction transverse to the strengthening member tostrengthen the composite slabs.

[0108] The void may be defined, by way of example, by a block ofmaterial that is adhered or otherwise secured to the base member.

[0109] A preferred material is a lightweight material such as styrene.

[0110] The void may also be defined, by way of further example, by avolume enclosed by (i) the base member, (ii) the sides of ribs of thebase member or other suitable members that are adjacent to a section ofthe base member that is between adjacent strengthening members, and(iii) a sheet of material spaced above the base member and extendingacross the section and contacting the adjacent ribs or other suitablemembers.

[0111] The void may also be defined, by way of further example, by avolume enclosed by (i) the base member and (ii) a shaped sheet, such asa curved sheet, of material that has sides that are retained by the ribsof the base member or other suitable retaining members.

[0112] The void may also be defined, by way of further example, by avolume enclosed by (i) the base member, and (ii) a channel member in anupturned position, with the base of the channel member spaced above thebase member and forming the top of the void and the sides of the channelmember extending downwardly and being structurally attached to the basemember and forming two other sides of the void.

[0113] Preferably the void is filled with fire resisting or retardingmaterial.

[0114] Preferably the inner surfaces of the channel member and thesurface of the base member that form the void are coated with a fireresisting or retarding material.

[0115] Preferably the void includes a sound absorbing material.

[0116] The structural formwork may also include:

[0117] (a) structural elements, such as steel bars or frameworks made upof a plurality of steel bars; and

[0118] (b) ties that mechanically couple the structural elements tosections of the base member of one structural formwork member or tosections of the base members of adjacent structural formwork membersthat are in overlapping relationship to minimise transverse deflectionof these sections when wet concrete is poured onto the structuralformwork member .

[0119] This feature relates particularly to those sections that arebetween strengthening members.

[0120] This feature can be used as an alternative to or in conjunctionwith the previously-described feature of the water impermeable void.

[0121] This feature is based on the applicant recognising thathydrostatic pressure of water in wet concrete acting against a basemember and the weight of the wet concrete are two particular factorsthat contribute to transverse deflection, i.e. downward bulging,particularly of sections of a base member that are between adjacentstrengthening members, in response to wet concrete loading.

[0122] As is described above, the applicant has found that the use ofstructural elements as described above minimises the adverse effect ofhydrostatic pressure and concrete weight by making it possible totransfer the load resulting from wet concrete to the adjacentstrengthening member.

[0123] The above-described feature is relevant particularly, although byno means exclusively, to situations in which there are two structuralformwork members laid side by side in overlapping relationship. In suchsituations there is a tendency for the lap joint between the two membersto separate in response to downward bulging of sections of the basemembers that include the lap joint.

[0124] According to the present invention there is also provided acomposite floor slab that includes the above-described structuralformwork member and a layer of hardened concrete on the member.

[0125] According to the present invention there is also provided acomposite slab in the form of a vertical wall panel that includes theabove-described structural formwork member and a layer of hardenedconcrete or other suitable castable panel material on the member.

[0126] The present invention is described further by way of example withreference to the accompanying drawings of which:

[0127]FIG. 1 is based on FIG. 1 of Australian patent 707101 and is aperspective view of one embodiment of a TRUSSDEK structural formworkmember;

[0128]FIG. 2 is an end elevation of an embodiment of a structuralformwork member in accordance with the present invention;

[0129]FIG. 3 is an end elevation of another embodiment of a structuralformwork member in accordance with the present invention;

[0130]FIG. 4 is an end elevation of another embodiment of a structuralformwork member in accordance with the present invention;

[0131]FIG. 5 is a perspective view of another embodiment of a structuralformwork member in accordance with the present invention;

[0132]FIG. 6 is a section along the line 6-6 of FIG. 5;

[0133]FIG. 7 is a perspective view of a strengthening member of anotherembodiment of a structural formwork member in accordance with thepresent invention;

[0134]FIG. 8 is a perspective view of a strengthening member of anotherembodiment of a structural formwork member in accordance with thepresent invention;

[0135]FIG. 9a is a perspective view of a strengthening member of anotherembodiment of a structural formwork member in accordance with thepresent invention;

[0136]FIG. 9b is a perspective view of one of the saddles of thestrengthening member shown in FIG. 9a; and

[0137]FIG. 10 is an end elevation of a strengthening member of anotherembodiment of a structural formwork member in accordance with thepresent invention.

[0138]FIG. 11 is an end elevation of an embodiment of a composite floorslab in accordance with the present invention that includes anotherembodiment of a structural formwork member in accordance with thepresent invention;

[0139]FIG. 12 is an end elevation of another embodiment of a compositefloor slab in accordance with the present invention that includesanother embodiment of a structural formwork member in accordance withthe present invention;

[0140]FIG. 13 is an end elevation of another embodiment of a compositefloor slab in accordance with the present invention that includesanother embodiment of a structural formwork member in accordance withthe present invention;

[0141]FIG. 14 is a side elevation of an end section of anotherembodiment of a structural formwork member in accordance with thepresent invention positioned on a floor support, the figure illustratingan embodiment of a bridging member in accordance with the presentinvention;

[0142]FIG. 15 is an end elevation of the arrangement shown in FIG. 14;

[0143]FIG. 16 is a side elevation similar to FIG. 14 which illustratesanother embodiment of a bridging member in accordance with the presentinvention;

[0144]FIG. 17 is an end elevation of the arrangement shown in FIG. 16;

[0145]FIG. 18 is a side elevation similar to the side elevations shownin FIGS. 14 and 16 which illustrates another embodiment of a bridgingmember in accordance with the present invention;

[0146]FIG. 19 is an end elevation of the arrangement shown in FIG. 18;

[0147]FIG. 20 is a side elevation similar to the side elevations shownin FIGS. 14, 16, and 18 which illustrates another embodiment of abridging member in accordance with the present invention;

[0148]FIG. 21 is an end elevation of the arrangement shown in FIG. 20along the line 21-21 in FIG. 20; and

[0149]FIG. 22 is an end elevation of another embodiment of a structuralformwork member in accordance with the present invention; and

[0150]FIG. 23 is an end elevation of another embodiment of a structuralformwork member in accordance with the present invention.

[0151] The structural formwork members shown in the figures aredescribed hereinafter in the context of structural formwork members thatcan be arranged side by side in overlapping relationship and supportedby temporary supports or permanent supports (such as steel beams) andare used in the construction of a composite floor slab that includes themembers and a layer of concrete on the members.

[0152]FIG. 1 is based on FIG. 1 of Australian patent 707101. The figureillustrates a typical TRUSSDEK structural formwork member 3.

[0153] The TRUSSDEK structural formwork member 3 shown in FIG. 1includes a base member in the form of a profiled steel sheet that hastwo parallel ribs 5 and three pans 6 that extend in the longitudinaldirection of the profiled steel sheet.

[0154] The sides of the base member include a male formation 38 and afemale formation 37 that enable adjacent sheets to be connected togetherwith leakproof lap joints by inserting the male formation 38 into thefemale formation 37.

[0155] The TRUSSDEK structural formwork member 3 further includes twostrengthening members, generally identified by the numeral 71 thatextend along the length of the base member. Each strengthening memberincludes a lattice girder formed from:

[0156] (a) a top chord element 7 extending parallel to the ribs 5; and

[0157] (b) a plurality of web chord elements 9 welded to the steel sheetand to the top chord element 7 and thereby interconnecting the steelsheet and the top chord element 7.

[0158] The chord elements 7, 9 are formed from steel bar.

[0159] The chord elements 7, 9 and the base member define two trusses.

[0160] The structural formwork members shown in FIGS. 2 to 23incorporate a number of improvements made by the inventors to theTRUSSDEK formwork member.

[0161] The structural formwork member shown in FIG. 2 includes a basemember in the form of a flat sheet 6 (rather than a profiled sheet) andstrengthening members 71 in the form of inverted channel members (ratherthan lattice girders) welded to the flat sheet.

[0162] Each channel member is formed from roll-formed steel sheet andhas a top wall 33 and two inclined sides 35 that are welded at lowerends of the base member.

[0163] The channel members are structural members that, with the basemember, are provided to sustain the effects of bending, vertical shear,and concentrated forces at supports.

[0164] In addition, the channel members and the base member define aseries of water impermeable voids 18.

[0165] The structural formwork members shown in FIGS. 3 and 4 aresimilar to that shown in FIG. 2.

[0166] The strengthening members of the structural formwork membersshown in FIGS. 3 and 4 further include top chord elements 39 in the formof steel plates welded to the channel members 71.

[0167] In addition, the structural formwork member shown in FIG. 4includes two different-sized channel members 71. This embodimentillustrates the flexibility of the subject invention.

[0168] The structural formwork member shown in FIGS. 5 and 6 includes abase member in the form of a profiled sheet that has a central rib 5 andtwo pans 6.

[0169] The structural formwork member also includes two strengtheningmembers, generally identified by the numeral 31, that extend along thelength of the base member.

[0170] Each strengthening member 31 is positioned in one of the pans 6and includes:

[0171] (a) an inverted channel member that is formed from roll-formedsteel sheet and has a top wall 33 and two inclined sides 35 that areconnected at their lower ends to the base member; and

[0172] (b) a top chord element 39 that is connected to the base 33 ofthe channel member.

[0173] The lower ends of the sides 35 of the channel member are formedas out-turned flanges 41 to maximise contact with the profiled steelsheet 3. The flanges 41 are welded and/or glued or otherwisestructurally connected to the base member.

[0174] Both sides 35 of the channel member include a series ofcorrugations 43 along the length of the sides 35 of the channel member.With reference to FIG. 6, the corrugations 43 include crests 45 andtroughs 47. Preferably, the depth D of the corrugations 43 is at least 6mm (note 3 mm each way about the sheet centreline) and the wavelength Wof the corrugations 43 is 30-60 mm. The corrugations 43 are formed sothat the crests 45 and the troughs 47 are transverse to the lengthwisedirection of the base member. The purpose of the corrugations 43 is toprovide resistance to lateral buckling of the formwork member and toincrease the bearing capacity at support reaction locations.

[0175] Both sides 35 of the channel member include openings 47 to allowaccess to the interior of the channel member, whereby wet concrete canflow into the volume defined by the channel member and the base memberduring construction of a composite slab and thereby fill the volume. Theopenings 47 are at about half height of the channel members. Preferablythe base of the openings 47 is above the height of the ribs 5. Theopenings are shown as slots. Preferably the slot width is not more than40% of the height of the channel members and the slot length of slotwidth ratio is not more than 2:1. Typically the slot width is 45 mm andthe length is 90 mm. Preferably there is at least 20 mm of channelmember above each slot—in order to provide sufficient shear resistance.

[0176] A number of the openings 47 in the sides 35 are aligned to alsoallow reinforcing bars/wires/cables (not shown) to be positioned toextend transversely through the channel member during construction of acomposite slab.

[0177] Both sides of the channel member also include a series of smallerholes 48 near the top of the channel members to allow air to escape fromthe channel member when wet concrete is flowing into the interior of thechannel member via major openings 47.

[0178] The top chord element 39 is in the form of a retangular crosssection steel bar that is welded or glued to the base 33 of the channelmember. The top chord element 39 is spaced above the base member by theheight H of the channel member.

[0179] The construction of the channel member from roll-formed steelsheet makes it possible to concentrate the steel of the strengtheningmember as far as possible above the base member while properlysupporting the steel in this position.

[0180] The embodiment of the strengthening member 31 shown in FIG. 7 issimilar in many respects to the embodiment shown in FIGS. 5 and 6.

[0181] For example, the embodiment shown in FIG. 7 includes aroll-formed channel member that has a base 33 and sides 35 without-turned flanges 41.

[0182] The main differences between the embodiments are that the topchord element 39 is in the form of a round steel bar that is supportedby web chords 40 that are welded to the sides 35 of the channel member.

[0183] The embodiment of the strengthening member 31 shown in FIG. 8 issimilar in many respects to the embodiment shown in FIGS. 5 and 7.

[0184] For example, the embodiment shown in FIG. 8 includes aroll-formed channel member that has a base 33 and sides 35 without-turned flanges 41 and openings 47 formed in the sides 35.

[0185] There are a number of differences between the embodiments.

[0186] For example, the embodiment shown in FIG. 8 also includesstiffening ribs 51 that are pressed from the planes of the sides 35 ofthe channel member rather than the corrugations 43 of the embodimentshown in FIGS. 5 and 6. The axes of the ribs 51 are transverse to thelengthwise extending direction of the profiled steel sheet 3 (notshown).

[0187] In addition, the base 33 of the channel member of the embodimentshown in FIG. 8 is shaped as a key-hole formation and the top chordelement 39 has a complementary circular cross-section and is received inand retained by the key-hole formation.

[0188] The embodiment of the strengthening member 31 shown in FIGS. 9aand 9 b is similar in many respects to the embodiments shown in FIGS. 5,6 and 8.

[0189] The main difference between the embodiments is that theembodiment shown in FIGS. 9a and 9 b includes detachable saddles 61 thatmount the top chord element 39 onto the channel member. The saddles 61straddle the base 33 of the channel member and engage the sides 35 ofthe channel member at spaced intervals along the length thereof. Thesaddles 61 also include semi-circular channels 63 that receive andretain the top chord element 39 by snap-fit engagement. The saddles 61engage the sides 35 of the channel member by means of inwardly directedtabs 69 that are formed in the legs 67 and extend into spaced openings(not shown) in the sides 35 of the channel member.

[0190] In the embodiment shown in FIG. 10 the top chord element 39 is inthe form of a plate that is welded to the base 33 of the channel member.Typically, the plate is 5 mm thick. The plate includes up-turned anddown-turned wings 79.

[0191] To maximise mechanical interlock with concrete the plate may bedeformed (for example, with upturned and downturned sections as shown inFIG. 10), rippled, and/or holed.

[0192] The plate is preferred in situations where high lateralstability, large flexual stiffness, and large tensile and compressivecapacity are required.

[0193] The structural formwork member shown in FIG. 11 includes a basemember in the form of a profiled steel sheet that has a series of ribs 5and pans 6 and two strengthening members 71 in the form of latticegirders that include two chord elements 7, wet chord elements 9, andbottom chord elements 8.

[0194] The strengthening members 71 are positioned so that eachstrengthening member 71 straddles an outer rib 5 of the base member withthe web chord elements 9 being welded to two pans 6 of the base member.The present invention is not limited to this arrangement and alsoextends to arrangements in which the strengthening members are locatedwholly in the pans 6—as shown in FIG. 5.

[0195] The width of the left-hand pan 6 as shown in FIG. 11 is selectedto be sufficiently wide and the position of the left-hand strengtheningmember is selected to be close to the rib 5 on that side so that thereis a clear space for shear connectors, such as headed studs (not shown),to be welded to an underlying steel beam (not shown) or fixed to otherfloor supports.

[0196] The width of the right-hand pan 6 as shown in FIG. 11 is selectedto be relatively narrow and, as a consequence, the right-handstrengthening member is close to the male formation 38. With thisarrangement, in use, the right-hand strengthening member will bepositioned close to and thereby support a joint between overlapping (andthereby interlocking) adjacent sheets.

[0197] One standard sized structural formwork member 3 has strengtheningmembers formed from 12 mm diameter steel bar and is constructed so thatthe top chord elements 7 are 120 mm above the pans 6, the centre tocentre spacing of the web chord elements 9 of each strengthening memberis 78 mm at their base, the centre to centre spacing of thestrengthening members (ie. the centre to centre spacing of the top chordelements 7) is 166 mm, and the left-hand strengthening member is 60 mmfrom the female formation 37.

[0198] The ribs 5 include downwardly converging sides 43 and a flat topwall 45. The downwardly converging sides 43 of the ribs 5 facilitateinterlocking of the base member with concrete to contribute toward thelongitudinal slip resistance developed between the base member and theconcrete. In addition, as is described hereinafter in more detail, thedownwardly converging sides 43 can be used to assist in retaining a voidformer 27 on the base member.

[0199] One standard sized structural formwork member 3 has ribs 5 thathave a height of 12 mm above the pans 6 and a top wall width of 50 mm.

[0200] The ribs 5 shown in FIG. 11 are small ribs.

[0201] The ribs 5 are small in the context of the height of the topchord element of the strengthening members above the pans 6.

[0202] The ribs 5 are also small in the context of the relationship ofthe height of the ribs 5 above the pans 6 and the height of the topchord elements 7 above the pans 6. Specifically, in the context of thestandard sized structural formwork member discussed above, therelationship is 12 mm versus 120 mm, ie the height of the ribs is 10% ofthe height of the top chord elements.

[0203] The ribs 5 are also small in the context of the width reductionof a flat sheet of steel strip that is required to form the structuralformwork member 3. Specifically, in the context of the above-describedstandard sized structural formwork member, a 630 mm wide flat strip wasroll-formed to form a 500 mm structural formwork member having theprofile shown in the figures, ie a width reduction of 79%.

[0204] The structural formwork member 3 shown in FIG. 11 also includes aplurality of retaining members 19 in the pans 6. The retaining members19 facilitate interlocking of the base member with concrete so that goodlongitudinal slip resistance can be developed between the base memberand the concrete and to prevent vertical separation of the base memberand hardened concrete. In addition, as described hereinafter, theretaining members can be used to assist in retaining a void former 27 tothe base member.

[0205] The structural formwork member 3 shown in FIG. 11 also includes avoid former 27 positioned in a section of the base member that isbetween the strengthening members 71.

[0206] The void former 27 is in the form of an inverted channel memberthat has a top wall 33 and two sides 35 that diverge from the top wall33 and contact the base member of the structural support member 3.

[0207] The void former 27 is retained on the base member by theretaining members 19. Specifically, the dimensions of the void former 27are selected so that there is an interference fit between the voidformers 27 and the retaining members 19.

[0208] Alternatively, or in addition, the void former 27 and theretaining members 19 may be provided with tabs (not shown) and openings(not shown) to facilitate interlocking of the void formers 27 and theretaining members.

[0209] The void former 27 may be open-ended.

[0210] Alternatively, the void former 27 may be formed with closed ends(not shown). For example, the ends of the void former 27 may be closedby inserts such as polystyrene plugs or thin steel plates.

[0211] When positioned on the base member as shown in FIG. 11, the voidformer 27 and the base member define a void in the section of the basemember that is between the strengthening members.

[0212] The purpose of the voids is to reduce the adverse effect of (i)hydrostatic pressure of water acting against the base member when wetconcrete is poured onto the section of the base member that is betweenthe strengthening members 71 and the base member and (ii) the weight ofthe wet concrete required to form a composite slab.

[0213] Preferably the voids achieve this purpose by taking up volume andtransferring load resulting from the wet concrete above the voids to thestrengthening members 71.

[0214] It is not essential that the voids be hollow spaces. In thiscontext, the relevant requirement is that a void be a space that remainsa space under the weight of wet concrete and cannot be penetrated by wetconcrete.

[0215] Thus, a void may be defined by a block of solid material, such asstyrene, that is secured to the base member.

[0216] It is also not essential that a void occupy the whole of thewidth of the section of the base member that is between thestrengthening members. The requirement is that the void extends across asubstantial part of the width of the section.

[0217] The structural formwork member shown in FIG. 11 forms part of acomposite floor slab. Specifically, the floor slab includes thestructural formwork member, a layer of concrete 4 on the member, andtransverse reinforcement 14.

[0218] The structural formwork members 3 shown in FIGS. 12 and 13 havethe same basic construction as the structural formwork member 3 shown inFIG. 11.

[0219] The main difference between the FIG. 11 and FIG. 12 structuralformwork members 3 is the construction of the void former 27.Specifically, the void former 27 is a relatively shallow void former 27in the form of a curved sheet of suitable material that is positioned sothat opposite sides are retained by the retaining members 19.

[0220] The use of a shallow void former 27 makes it possible to use thestructural formwork member 3 in the construction of a composite slabthat will be subject to 2-way bending action. Specifically, as shown,the shallow void former 27 makes it possible to locate transversepre-stressing ducts and cables 46 in the composite slab—as required whenthere is 2-way bending action. Whilst not shown in FIG. 12, butnevertheless as shown in FIG. 13, upper and lower transversereinforcement 49 may be used as an alternative to the use of transversepre-stressing. The shallow void former 27 also makes it possible tolocate a longitudinal duct 44 housing service cables sufficiently lowdown in the slab.

[0221] The main difference between the FIGS. 11 and 12 and the FIG. 13structural formwork members 3 is that the FIG. 13 member includes athird strengthening member straddling the central rib 5 and thereforedoes not require a void former 27.

[0222]FIG. 13 also illustrates the preferred locations of headed studs48 that may be used to secure the formwork members 3 to floor supports,such as steel beams (not shown).

[0223] The structural formwork members 3 shown in FIGS. 2 to 13 furtherinclude bridging members at one or both ends or at positions along thelength of the structural formwork member to facilitate optimum loadtransfer in use of the member to temporary or permanent supports.Various embodiments of bridging members are described hereinafter withreference to FIGS. 14 to 21. The bridging members are generallyidentified by the numeral 11 in these figures.

[0224] In use, in order to construct a floor:

[0225] (a) a number of the structural formwork members are positioned torest on temporary or permanent floor supports 13, such as vertical wallsand horizontal beams, with the bridging members 11 enabling loadtransfer from the strengthening members 71 to the floor supports 13; and

[0226] (b) concrete is poured onto the formwork members and forms aplurality of composite floor slabs (as shown in FIGS. 11 to 13).

[0227] Depending on the requirements in any given situation, thestructural formwork members may extend across a single span betweenadjacent floor supports 13 and be supported only at the ends by thesefloor supports 13 or may extend across multiple spans and be supportedat the ends by the outermost floor supports and at one or more locationsalong the length of the structural formwork members by the intermediatefloor support or supports 13.

[0228] In practice, the spans between floor supports 13 may be 5 m ormore. Particularly with spans of this order, it is important that therebe optimum load transfer from the structural formwork members to thefloor supports 13.

[0229] Typically, structural formwork members are constructed away froma building site and are transported to the site. Typically, thestrengthening members include a basic unit of length L (as can be seenin FIG. 14) that is repeated along the length of the structural formworkmembers.

[0230] Depending on the length of a structural formwork member, thestrengthening member 71 at one or both end sections of the member that,in use, rest on floor supports 13 may be an end of a unit or part wayalong the length of a unit. As indicated above, these are importantconsiderations because the structure of the strengthening member 71 atend or intermediate sections of a structural formwork member that restdirectly on floor supports 13 can affect load transfer between thestructural formwork member and the floor supports 13.

[0231] More specifically, less than optimum load transfer may lead toreduced strength and excessive deflection or local deformation of thestructural formwork member, particularly when concrete is poured ontothe member to form a composite floor slab.

[0232] As illustrated in the four embodiments shown in FIGS. 14/15,16/17, 18/19, and 20/21 the bridging member 11 is connected to at leastone end of a structural formwork member and/or at one or more locationsbetween the ends of the structural formwork member to enable optimumload transfer from the strengthening member 71 to the floor supports.

[0233] In the case of the FIGS. 14/15 embodiment, the bridging member 11is a triangular frame 15 formed by bending a length of steel bar. Theframe 15 is connected to the structural formwork member 3 by welding:

[0234] (a) apex 17 of the frame 15 to the top and web chord elements7,9; and

[0235] (b) apices 19, 21 of the frame 15 to the bottom chord elements 8.

[0236] The position of the frame 15 is selected so that, in use, thebase 23 of the frame 15 is above the floor support 13.

[0237] Optimum positioning of the frame 15 may necessitate cuttingand/or bending one or more of the top chord element 7, the bottom chordelement 8, and the web chord elements 9. The dotted line identified bythe numeral 23 in FIG. 14 illustrates the position of the web chordelements 9 in the as-constructed structural formwork member. It isevident from the figure that in order to correctly position the frame 15it was necessary to cut the top and web chord elements 7, 9 and to bendthe web chord elements 9 upwardly to contact the top chord element 7.

[0238] In the case of the FIGS. 16/17 embodiment the bridging member 11includes:

[0239] (a) a mounting block 29 that has a hollow core that can receivethe top chord element 7 and can be slid along the top chord element 7 toa required position, and then bear against web chord element 9, or elsebe swaged, welded, or otherwise connected to the top chord element 7 inthat position;

[0240] (b) a pair of chord elements 37 each connected at one end to theblock 29 and arranged to extend downwardly from the block 29; and

[0241] (c) a pair of bottom chord elements 51 that are parallel to theaxis of the core of the block 29 and can be swaged, welded, or otherwiseconnected to the bottom chord elements 8 of the formwork member 3.

[0242] In the case of the FIGS. 18/19 embodiment the bridging includes aplate 35 that is spot welded to the undersurface of the pan 6 of theformwork member 3.

[0243] In the case of the FIGS. 20/21 embodiment the bridging member 11is the same triangular frame construction as shown in the FIGS. 14/15embodiment. In the case of the FIGS. 20/21 embodiment the frame 15 ispositioned so that the base of the frame is above the intermediate floorsupport 13 shown in the figures.

[0244] The structural formwork members 3 shown in FIGS. 22 and 23 arethe same basic construction in many respects as the structural formworkmembers 3 shown in the previously-described figures.

[0245]FIGS. 22 and 23 illustrate alternative options to minimisetransverse deflection, ie downward bulging, of sections of profiledsteel sheets that are between adjacent strengthening members.

[0246]FIGS. 22 and 23 illustrate overlapping structural formworkmembers. In these situations, the sections of the profiled steel sheetsthat are in question are the adjacent side sections of the overlappingsheets, including male formations 38 and female formations 37 that formlap joints 61 of the sheets.

[0247] In the arrangement shown in FIG. 22 the formwork member includesa structural element in the form of a steel bar 63 that is connected atopposite ends to the adjacent strengthening members and a centrallylocated tie 65 that is connected at one end to the bar 63 and is formedas a hook that engages the lap joint 61.

[0248] In the arrangement shown in FIG. 23 the structural formworkmember includes a structural element in the form of a framework of steelbars 63 that are arranged in a pyramid shape with a central apex locatedabove the lap joint 61 and the steel bars extending downwardly andoutwardly with the lower ends of the bars 63 butting against ribs 5 thatare immediately adjacent the strengthening members.

[0249] In both arrangements shown in FIGS. 22 and 23, the steel bars 63and the framework of steel bars 63 transfer load to the strengtheningmembers 71 and thereby resist downward deflection of the overlappingsections of the profiled steel sheets when wet concrete is poured ontothe sheets.

[0250] The above-described embodiments are examples of many possibleembodiments of structural formwork members in accordance with thepresent invention.

[0251] Many modifications may be made to the preferred embodiments ofthe present invention that are described with reference to theaccompanying drawings without departing from the spirit and scope of theinvention.

[0252] By way of example, whilst the void formers 27 shown in FIGS. 11and 12 are retained on the base member of the structural formworkmembers 3 by engaging the retaining members 19, the present invention isnot so limited and extends to any suitable means of retaining the voidformers to the base member.

[0253] By way of further example, whilst the base member is described asbeing formed from steel sheet, the present invention is not so limitedand the base member may be formed from any suitable metallic ornon-metallic material.

1. A structural formwork member comprising: (a) a base member in theform of a profiled metal sheet, the base member including parallel ribsand plurality of pans between the ribs, the ribs being small ribs; and(b) at least one strengthening member that is structurally connected tothe base member.
 2. The structural formwork member defined in claim 1wherein the height of the ribs above the pans of the base member is nomore than 20 mm.
 3. The structural formwork member defined in claim 1wherein the height of the ribs above the pans of the base member is nomore than 15 mm.
 4. The structural formwork member defined in claim 1wherein the height of the ribs above the pans of the base member is nomore than 10 mm.
 5. The structural formwork member defined in claim 1wherein the height of the ribs above the pans of the base member is nomore than 20% of the height of the strengthening member above the pans.6. The structural formwork member defined in claim 5 wherein the heightof the ribs of the base member above the pans is no more than 15% of theheight of the strengthening member above the pans.
 7. The structuralformwork member defined in claim 1 wherein the height and the number ofthe ribs of the base member is selected so that the width of the basemember is at least 80% of the width of a flat sheet prior to forming theribs in the flat sheet and producing the base member.
 8. The structuralformwork member defined in claim 1 wherein the strengthening memberincludes a lattice girder formed from a top chord element that is spacedabove the base member and web chord elements that are connected to thetop chord element and to the ribs and/or pans of the base member.
 9. Thestructural formwork member defined in claim 8 wherein the lattice girderalso includes bottom chord elements that are parallel to the top chordelement and are connected to the web chord elements.
 10. The structuralformwork member defined in claim 1 wherein the strengthening member isin the form of an inverted channel member.
 11. The structural formworkmember defined in claim 10 wherein the inverted channel member has a topwall and two sides, with the sides being connected to the top wallmember and the base being spaced above the base member.
 12. A structuralformwork member comprising: (a) a base member in the form of a metalsheet; and (b) at least one strengthening member in the form of aninverted channel member that is structurally connected to the basemember.
 13. The structural formwork member defined in claim 12 whereinthe base member is in the form of a flat metal sheet.
 14. The structuralformwork member defined in claim 12 wherein the base member is in theform of a profiled metal sheet and includes parallel ribs that extendalong the length of the base member and a plurality of pans between theribs.
 15. The structural formwork member defined in claim 14 wherein theribs are small ribs.
 16. The structural formwork member defined in claim12 wherein the channel member has a top wall and two sides, with thesides being connected to the base member and the base being spaced abovethe top wall member.
 17. The structural formwork member defined in claim12 wherein the channel member is formed from a roll-formed metal sheet.18. The structural formwork member defined in claim 17 wherein theroll-formed sheet is 0.6-1.2 mm thick.
 19. The structural formworkmember defined in claim 17 wherein the thickness of the roll-formedsheet is 0.6-0.8 mm.
 20. The structural formwork member defined in claim12 wherein the height of the channel member is 80-240 mm.
 21. Thestructural formwork member defined in claim 12 wherein the height of thechannel member is 130-240 mm.
 22. The structural formwork member definedin claim 12 wherein the width of the channel member, measured betweenthe connections of the sides of the channel member to the base member,is 90-190 mm.
 23. The structural formwork member defined in claim 12wherein the sides of the channel member have outwardly turned flanges toimprove the connections between the sides of the channel member and thebase member.
 24. The structural formwork member defined in claim 12wherein one or both sides of the channel member include sections thatare pressed or otherwise formed out of the plane of the side or sides toprovide resistance to local buckling of the structural formwork memberand to increase the shear capacity of the structural formwork member.25. The structural formwork member defined in claim 24 wherein thepressed sections are ribs or corrugations in the side or sides.
 26. Thestructural formwork member defined in claim 25 wherein the axes of theribs extend transversely to the lengthwise direction of the base member.27. The structural formwork member defined in claim 25 wherein thecrests and the troughs of the corrugations extend transversely to thelengthwise direction of the base member.
 28. The structural formworkmember defined in claim 12 wherein the channel member and the basemember define a water impermeable void to minimise transverse deflectionof the structural formwork member when wet concrete is poured onto themember in the construction of a composite slab and/or to provide anaccess pathway for building services, such as telecommunications cables,in the completed composite slab.
 29. The structural formwork memberdefined in claim 12 wherein one or both sides of the channel memberinclude openings to allow access to the interior of the channel member,whereby wet concrete can flow into the volume defined by the channelmember and the base member during construction of a composite slab. 30.The structural formwork member defined in claim 12 wherein the sides ofthe channel member include aligned openings to allow reinforcingbars/wires/cables to be positioned to extend transversely through thechannel member during construction of a composite slab.
 31. Thestructural formwork member defined in claim 12 wherein the channelmember further includes a top chord element mounted to or retained bythe channel member.
 32. The structural formwork member defined in claim31 wherein the top chord element is a bar or a rod or a plate.
 33. Thestructural formwork member defined in claim 32 wherein the plate hasup-turned and/or down-turned sections to improve mechanical interlock ofthe structural formwork member with concrete in a composite slab.
 34. Astructural formwork member comprising: (a) a base member in the form ofa metal sheet; (b) at least one strengthening member that isstructurally connected to the base member; and (c) a bridging memberthat is connected to one or both ends of the member and/or at one ormore locations along the length of the member to enable direct loadtransfer from the strengthening member to temporary or permanentsupports for the structural formwork member.
 35. The structural formworkmember defined in claim 34 wherein the bridging member is in the form ofa chord element connected to the strengthening member.
 36. Thestructural formwork member defined in claim 35 wherein the chord elementis in the form of a frame.
 37. The structural formwork member defined inclaim 35 wherein the chord element includes a means that permitsadjustable connection of the chord element to the strengthening member.38. The structural formwork member defined in claim 34 wherein thebridging member is in the form of a panel formed from steel sheet orplate.
 39. The structural formwork member defined in claim 34 whereinthe bridging member is in the form of an elongate member, such as a beamand a plate, connected to the base member of the structural formworkmember.
 40. The structural formwork member defined in claim 34 whereinthe strengthening member includes a lattice girder formed from a topchord element that is spaced above the base member and web chordelements that are connected to the top chord element and to the basemember.
 41. The structural formwork member defined in claim 40 whereinthe lattice girder also includes bottom chord elements that are parallelto the top chord element and are connected to the web chord elements.42. The structural formwork member defined in claim 34 wherein thestrengthening member is in the form of an inverted channel member. 43.The structural formwork member defined in claim 42 wherein the invertedchannel member has a top wall and two sides, with the sides beingconnected to the top wall member and the base being spaced above thebase member.
 44. A structural formwork member comprising: (a) a basemember in the form of a metal sheet; (b) a plurality of strengtheningmembers that are structurally connected to the base member; and (c) awater impermeable void that contacts a section of the base memberbetween adjacent strengthening members to minimise transverse deflectionof the section when wet concrete is poured onto the structural formworkmember.
 45. The structural formwork member defined in claim 44 whereinthe void does not function as a structural member.
 46. The structuralformwork member defined in claim 44 wherein the void extends across asubstantial part of the width of the section of the base member that isbetween adjacent strengthening members.
 47. The structural formworkmember defined in claim 44 wherein the void extends across at least 70%of the section of the base member that is between adjacent strengtheningmembers.
 48. The structural formwork member defined in claim 44, furthercomprising a plurality of voids spaced along the length of the sectionof the base member that is between adjacent strengthening members. 49.The structural formwork member defined in claim 44, further comprising asingle void extending along the length of the section of the base memberthat is between adjacent strengthening members.
 50. The structuralformwork member defined in claim 44 wherein the void is small in termsof height so as to make it possible to use the member in theconstruction of composite slabs that will be subject to significant2-way bending action and therefore require a significant amount ofreinforcement or pre-stressing in a direction transverse to thestrengthening member to strengthen the composite slab.
 51. Thestructural formwork member defined in claim 44 wherein the void isdefined by a block of material that is adhered or otherwise secured tothe base member.
 52. The structural formwork member defined in claim 44wherein the base member is in the form of a profiled metal sheet thathas lengthwise extending ribs and pans between the ribs.
 53. Thestructural formwork member defined in claim 52 wherein the void isdefined by a volume enclosed by (i) the base member, (ii) the sides ofribs of the base member or other suitable members that are adjacent to asection of the base member that is between adjacent strengtheningmembers, and (iii) a sheet of material spaced above the base member andextending across the section and contacting the adjacent ribs or othersuitable members.
 54. The structural formwork member defined in anyclaim 52 wherein the void is defined by a volume enclosed by (i) thebase member and (ii) a shaped sheet of material that has sides that areretained by the ribs of the base member or other suitable retainingmembers.
 55. The structural formwork member defined in claim 52 whereinthe void is defined, by way of further example, by a volume enclosed by(i) the base member, and (ii) a channel member in an upturned position,with the base of the channel member spaced above the base member andforming the top of the void and the sides of the channel memberextending downwardly and being structurally attached to the base memberand forming two other sides of the void.
 56. (canceled)
 57. (canceled)58. A composite floor slab comprising: (a) a structural formwork memberwhich comprises: (i) a base member in the form of a profiled metalsheet, the base member including parallel ribs and a plurality of pansbetween the ribs, the ribs being small ribs; and (ii) at least onestrengthening member that is structurally connected to the base member;and (b) a layer of hardened concrete disposed on the structural formworkmember.
 59. A composite slab in the form of a vertical wall panel,comprising: (a) a structural formwork member which comprises: (i) a basemember in the form of a profiled metal sheet, the base member includingparallel ribs and a plurality of pans between the ribs, the ribs beingsmall ribs; and (ii) at least one strengthening member that isstructurally connected to the base member; and (b) a layer of hardenedconcrete or other suitable castable panel material disposed on thestructural formwork member.